Researchers say it might be time to resurrect psychedelics for psychiatry.

Before they were banned about a half century ago, psychedelic drugs like LSD and psilocybin showed promise for treating conditions including alcoholism and some psychiatric disorders.

Experts now say regulators, scientists, and the public should “revisit drugs that were once used but fell out of use because of political machinations, especially the war on drugs”.

Dr David Nutt, a professor and neuropharmacologist at Imperial College London, says the scientific world has learned much in the decades since psychedelics were banned.

“There's mechanistic evidence in humans of how these drugs affect the brain,” he said in a new article for the journal Cell.

“By back-translating from humans to rodent models, we can see how these drugs produce the powerful neuroplastic changes that explain the long-term alterations we see in humans.”

Brain imaging has shown that the activity of psychedelic drugs is mediated through a receptor in brain cells called 5-HT2A. There is a high density of these receptors in the “thinking parts of the brain”, Dr Nutt explains.

The key part of the brain that appears to be disrupted by the use of psychedelics is the default mode network.

This area is active during thought processes like daydreaming, recalling memories, and thinking about the future - when the mind is wandering, essentially. It is also an area that is overactive in people with disorders like depression and anxiety.

Psychedelics appear to have long-term effects on the brain by activating 5-HT2A receptors in this part of the brain.

More research is needed to understand why these effects last so long, both from a psychological perspective and in terms of altered brain functioning and anatomy.

Psilocybin-assisted therapy for treatment-resistant depression has been granted breakthrough therapy designation from the US Food and Drug Administration. This came about through lobbying by COMPASS Pathways, a for-profit company that is leading clinical research to test the safety and efficacy of such treatments.

Dr Nutt says there is evidence of potential for psychedelic drugs in the treatment of alcoholism, which is the cause of about one in 20 deaths worldwide every year.

“If we changed the regulations, we would have an explosion in this kind of research,” Dr Nutt says.

“An enormous opportunity has been lost, and we want to resurrect it. It's an outrageous insult to humanity that these drugs were abandoned for research just to stop people from having fun with them. The sooner we get these drugs into proper clinical evaluation, the sooner we will know how best to use them and be able to save lives.”